This invention relates to high intensity discharge (HID) lamps, more particularly high pressure sodium lamps and metal halide lamps containing sodium halides, both of which require a high voltage for starting and which also exhibit a tendency for the migration of sodium ions through the arc tube wall.
Different types of high intensity discharge lamps share common design requirements; in the past these criteria were addressed on a case-by-case basis for each particular lamp type. Normally each HID lamp design must employ a starting means, a means for preventing the deleterious effect of the starting aid after lamp start-up during normal operation, and means for controlling the migration of sodium through the arc tube.
The prior art utilized numerous devices for meeting the above requirements for various lamp types, as represented by the following:
U.S. Pat. No. 3,872,340 dated Mar. 18, 1975 to Collins discloses the use of an ignition coil to aid in the starting of high pressure sodium lamps. The ignition coil is made of two separate bimetallic pieces which upon lamp heat-up physically remove themselves from proximity of the arc tube as a consequence of their bimetallic construction and geometric configuration.
U.S. Pat. No. 3,900,753 dated Aug. 19, 1975 to Richardson comprises a high pressure sodium lamp composed of an arc tube containing a Penning gas mixture and an ignition coil wrapped about the outside of the arc tube. The ignition coil is electrically removed from its source of main electrode voltage after lamp heat-up by a thermal switch.
U.S. Pat. No. 4,037,129 dated July 19, 1977 to Zack et al. discloses a high pressure sodium lamp with a multiple turn ignition coil covering greater than 10% of the arc tube length. The ignition coil is electrically removed from its source of main electrode voltage after lamp heat-up by a thermal switch.
U.S. Pat. No. 4,117,371 dated Sept. 26, 1979 to Van Vliet et al. comprises a high pressure sodium lamp using a multiple turn igntion coil covering less than 10% of the arc tube length. The ignition coil is electrically removed from its source of main electrode voltage after lamp heat-up by a temperature dependent resistor.
U.S. Pat. No. 4,179,640 dated Dec. 18, 1979 to Larson shows a high pressure sodium lamp using an ignition coil that is electrically removed from its source of main electrode voltage after the main arc discharge has commenced by a high impedance capacitor or resistor.
U.S. Pat. No. 3,619,711 dated Nov. 9, 1971 to Freese discloses the use of an auxiliary electrode with a rectifying diode and current limiting resistor electrically connected between the main electrode voltage for use in a metal halide lamp.
U.S. Pat. No. 3,706,898 dated Dec. 19, 1972 to Peterson discloses a metal halide lamp that employs an auxiliary electrode to assist starting the lamp. Deleterious effects of the auxiliary electrode after start-up, during normal lamp operation, is prevented by an AC limiting, DC filtering capacitor connected thereto.
U.S. Pat. Nos. 3,900,762 dated Aug. 19, 1975 to Freese et al.; 3,982,154 dated Sept. 21, 1976 to Mize et al.; 4,007,397 dated Feb. 8, 1977 to Lake; and 4,097,777 dated June 27, 1978 to Bacharowski all reveal variations of metal halide lamps that include an auxiliary electrode and rectifying diode that perform the dual functions of acting as a voltage doubling circuit to aid in start-up and rectifying auxiliary electrode voltage to prevent degradation of the lamp during normal operation after start-up.